[nstevens]

I'd say the two most important libraries for our app have been Retrofit & Picasso.  Both are built on RxAndroid so using it as well is a natural extension.  I think most people would probably only need RxAndroid or otto but we've enjoyed using both.  We mainly use the former for chaining network calls and the latter to maintain a bus of state updates.

Dagger 1.x (which we currently use) certainly helped slim down code size but it's mix of compile time and run time injection made using tools like Proguard a bit messy.  We haven't made the jump yet but it seems like Dagger 2.x solves for this: https://github.com/google/dagger

Butterknife is just plain useful to avoid a ton of view boilerplate code.

Our app is admittedly not too complicated but so far we haven't seen any performance issues.